Functions (Apache Calcite API)

java.lang.Object
- org.apache.calcite.linq4j.function.Functions

public abstract class Functions
extends Object

Utilities relating to functions.

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`private static class`	`Functions.ArrayEqualityComparer` Array equality comparer.
`private static class`	`Functions.GeneratingList<E>` List that generates each element using a function.
`private static class`	`Functions.IdentityEqualityComparer` Identity equality comparer.
`private static class`	`Functions.Ignore<R,T0,T1>` Ignore.
`private static class`	`Functions.NullsFirstComparator` Nulls first comparator.
`private static class`	`Functions.NullsFirstReverseComparator` Nulls first reverse comparator.
`private static class`	`Functions.NullsLastComparator` Nulls last comparator.
`private static class`	`Functions.NullsLastReverseComparator` Nulls last reverse comparator.
`private static class`	`Functions.SelectorEqualityComparer<T,T2>` Selector equality comparer.

Field Summary

Fields
Modifier and Type	Field and Description
`private static EqualityComparer<Object[]>`	`ARRAY_COMPARER`
`private static Function1`	`CONSTANT_NULL_FUNCTION1`
`static Map<Class<? extends Function>,Class>`	`FUNCTION_RESULT_TYPES`
`private static Map<Class,Class<? extends Function>>`	`FUNCTION1_CLASSES`
`private static EqualityComparer<Object>`	`IDENTITY_COMPARER`
`private static Comparator`	`NULLS_FIRST_COMPARATOR`
`private static Comparator`	`NULLS_FIRST_REVERSE_COMPARATOR`
`private static Comparator`	`NULLS_LAST_COMPARATOR`
`private static Comparator`	`NULLS_LAST_REVERSE_COMPARATOR`
`private static Function1`	`TO_STRING_FUNCTION1`

Constructor Summary

Constructors
Modifier Constructor and Description

private Functions()

Constructors
Modifier	Constructor and Description
`private`	`Functions()`

Method Summary

All Methods Static Methods Concrete Methods Deprecated Methods
Modifier and Type	Method and Description
`static <T1> Function1<T1,Double>`	`adapt(DoubleFunction1<T1> f)` Adapts a `DoubleFunction1` (that returns a `double`) to an `Function1` returning a `Double`.
`static <T1> Function1<T1,Float>`	`adapt(FloatFunction1<T1> f)` Adapts a `FloatFunction1` (that returns a `float`) to an `Function1` returning a `Float`.
`static <T1> Function1<T1,Integer>`	`adapt(IntegerFunction1<T1> f)` Adapts an `IntegerFunction1` (that returns an `int`) to an `Function1` returning an `Integer`.
`static <T1,R> List<R>`	`adapt(List<T1> list, Function1<T1,R> f)` Deprecated. Use `Lists.transform(java.util.List<F>, com.google.common.base.Function<? super F, ? extends T>)`
`static <T1> Function1<T1,Long>`	`adapt(LongFunction1<T1> f)` Adapts a `LongFunction1` (that returns a `long`) to an `Function1` returning a `Long`.
`static <T,R> List<R>`	`adapt(T[] ts, Function1<T,R> f)` Deprecated. Use `Lists.transform(java.util.List<F>, com.google.common.base.Function<? super F, ? extends T>)` and `Arrays.asList(Object[])`
`static <E> boolean`	`all(List<? extends E> list, Predicate1<E> predicate)` Returns whether `predicate` is true for all elements of `list`.
`static <T1,R> List<R>`	`apply(List<T1> list, Function1<T1,R> f)` Creates a copy of a list, applying a function to each element.
`static <T> EqualityComparer<T[]>`	`arrayComparer()` Returns an `EqualityComparer` that works on arrays of objects.
`static <T,R> Function1<T,R>`	`constant(R r)` Returns a 1-parameter function that always returns the same value.
`static <T,R> Function1<T,R>`	`constantNull()` Returns a 1-parameter function that always returns null.
`static <E> boolean`	`exists(List<? extends E> list, Predicate1<E> predicate)` Returns whether there is an element in `list` for which `predicate` is true.
`static <T> Predicate1<T>`	`falsePredicate1()` A predicate with one parameter that always returns `true`.
`static <T1,T2> Predicate2<T1,T2>`	`falsePredicate2()` A predicate with two parameters that always returns `false`.
`static <E> List<E>`	`filter(List<E> list, Predicate1<E> predicate)` Returns a list that contains only elements of `list` that match `predicate`.
`static Class<? extends Function>`	`functionClass(Type aClass)` Returns the appropriate interface for a lambda function with 1 argument and the given return type.
`static <E> List<E>`	`generate(int size, Function1<Integer,E> fn)` Returns a list generated by applying a function to each index between 0 and `size` - 1.
`static <T> EqualityComparer<T>`	`identityComparer()` Returns an `EqualityComparer` that uses object identity and hash code.
`static <TSource> Function1<TSource,TSource>`	`identitySelector()`
`static <R> Function0<R>`	`ignore0()` Returns a function of arity 0 that does nothing.
`static <R,T0> Function1<R,T0>`	`ignore1()` Returns a function of arity 1 that does nothing.
`static <R,T0,T1> Function2<R,T0,T1>`	`ignore2()` Returns a function of arity 2 that does nothing.
`private static <K,V> Map<V,K>`	`inverse(Map<K,V> map)`
`private static <K,V> Map<K,V>`	`map(K k, V v, Object... rest)`
`static <T extends Comparable<T>> Comparator<T>`	`nullsComparator(boolean nullsFirst, boolean reverse)` Returns a `Comparator` that handles null values.
`static <T,T2> Predicate1<T>`	`ofTypePredicate(Class<T2> clazz)` Creates a predicate that returns whether an object is an instance of a particular type or is null.
`static <T,T2> EqualityComparer<T>`	`selectorComparer(Function1<T,T2> selector)` Returns an `EqualityComparer` that uses a selector function.
`private static <T> Predicate1<T>`	`toPredicate(Function1<T,Boolean> function)` Converts a 1-parameter function to a predicate.
`static <T1,T2> Predicate2<T1,T2>`	`toPredicate(Function2<T1,T2,Boolean> function)` Converts a 2-parameter function to a predicate.
`static <T1,T2> Predicate2<T1,T2>`	`toPredicate2(Predicate1<T1> p1)`
`static <TSource> Function1<TSource,String>`	`toStringSelector()` Returns a selector that calls the `Object.toString()` method on each element.
`static <T> Predicate1<T>`	`truePredicate1()` A predicate with one parameter that always returns `true`.
`static <T1,T2> Predicate2<T1,T2>`	`truePredicate2()` A predicate with two parameters that always returns `true`.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - FUNCTION_RESULT_TYPES
```
public static final Map<Class<? extends Function>,Class> FUNCTION_RESULT_TYPES
```
  - FUNCTION1_CLASSES
```
private static final Map<Class,Class<? extends Function>> FUNCTION1_CLASSES
```
  - NULLS_FIRST_COMPARATOR
```
private static final Comparator NULLS_FIRST_COMPARATOR
```
  - NULLS_LAST_COMPARATOR
```
private static final Comparator NULLS_LAST_COMPARATOR
```
  - NULLS_LAST_REVERSE_COMPARATOR
```
private static final Comparator NULLS_LAST_REVERSE_COMPARATOR
```
  - NULLS_FIRST_REVERSE_COMPARATOR
```
private static final Comparator NULLS_FIRST_REVERSE_COMPARATOR
```
  - IDENTITY_COMPARER
```
private static final EqualityComparer<Object> IDENTITY_COMPARER
```
  - ARRAY_COMPARER
```
private static final EqualityComparer<Object[]> ARRAY_COMPARER
```
  - CONSTANT_NULL_FUNCTION1
```
private static final Function1 CONSTANT_NULL_FUNCTION1
```
  - TO_STRING_FUNCTION1
```
private static final Function1 TO_STRING_FUNCTION1
```
- Constructor Detail
  - Functions
```
private Functions()
```
- Method Detail
  - map
```
private static <K,V> Map<K,V> map(K k,
                                  V v,
                                  Object... rest)
```
  - inverse
```
private static <K,V> Map<V,K> inverse(Map<K,V> map)
```
  - constant
```
public static <T,R> Function1<T,R> constant(R r)
```
    Returns a 1-parameter function that always returns the same value.
  - constantNull
```
public static <T,R> Function1<T,R> constantNull()
```
    Returns a 1-parameter function that always returns null.
  - truePredicate1
```
public static <T> Predicate1<T> truePredicate1()
```
    A predicate with one parameter that always returns true.
    
    Type Parameters:
    
    T - First parameter type
    
    Returns:
    
    Predicate that always returns true
  - falsePredicate1
```
public static <T> Predicate1<T> falsePredicate1()
```
    A predicate with one parameter that always returns true.
    
    Type Parameters:
    
    T - First parameter type
    
    Returns:
    
    Predicate that always returns true
  - truePredicate2
```
public static <T1,T2> Predicate2<T1,T2> truePredicate2()
```
    A predicate with two parameters that always returns true.
    
    Type Parameters:
    
    T1 - First parameter type
    
    T2 - Second parameter type
    
    Returns:
    
    Predicate that always returns true
  - falsePredicate2
```
public static <T1,T2> Predicate2<T1,T2> falsePredicate2()
```
    A predicate with two parameters that always returns false.
    
    Type Parameters:
    
    T1 - First parameter type
    
    T2 - Second parameter type
    
    Returns:
    
    Predicate that always returns false
  - identitySelector
```
public static <TSource> Function1<TSource,TSource> identitySelector()
```
  - toStringSelector
```
public static <TSource> Function1<TSource,String> toStringSelector()
```
    Returns a selector that calls the Object.toString() method on each element.
  - ofTypePredicate
```
public static <T,T2> Predicate1<T> ofTypePredicate(Class<T2> clazz)
```
    Creates a predicate that returns whether an object is an instance of a particular type or is null.
    
    Type Parameters:
    
    T - Type of objects to test
    
    T2 - Desired type
    
    Parameters:
    
    clazz - Desired type
    
    Returns:
    
    Predicate that tests for desired type
  - toPredicate2
```
public static <T1,T2> Predicate2<T1,T2> toPredicate2(Predicate1<T1> p1)
```
  - toPredicate
```
public static <T1,T2> Predicate2<T1,T2> toPredicate(Function2<T1,T2,Boolean> function)
```
    Converts a 2-parameter function to a predicate.
  - toPredicate
```
private static <T> Predicate1<T> toPredicate(Function1<T,Boolean> function)
```
    Converts a 1-parameter function to a predicate.
  - functionClass
```
public static Class<? extends Function> functionClass(Type aClass)
```
    Returns the appropriate interface for a lambda function with 1 argument and the given return type.
    For example:
    functionClass(Integer.TYPE) returns IntegerFunction1.class functionClass(String.class) returns Function1.class
    
    Parameters:
    
    aClass - Return type
    
    Returns:
    
    Function class
  - adapt
```
public static <T1> Function1<T1,Integer> adapt(IntegerFunction1<T1> f)
```
    Adapts an IntegerFunction1 (that returns an int) to an Function1 returning an Integer.
  - adapt
```
public static <T1> Function1<T1,Double> adapt(DoubleFunction1<T1> f)
```
    Adapts a DoubleFunction1 (that returns a double) to an Function1 returning a Double.
  - adapt
```
public static <T1> Function1<T1,Long> adapt(LongFunction1<T1> f)
```
    Adapts a LongFunction1 (that returns a long) to an Function1 returning a Long.
  - adapt
```
public static <T1> Function1<T1,Float> adapt(FloatFunction1<T1> f)
```
    Adapts a FloatFunction1 (that returns a float) to an Function1 returning a Float.
  - adapt
```
@Deprecated
public static <T1,R> List<R> adapt(List<T1> list,
                                               Function1<T1,R> f)
```
    Deprecated. Use Lists.transform(java.util.List<F>, com.google.common.base.Function<? super F, ? extends T>)
    
    Creates a view of a list that applies a function to each element.
  - adapt
```
@Deprecated
public static <T,R> List<R> adapt(T[] ts,
                                              Function1<T,R> f)
```
    Deprecated. Use Lists.transform(java.util.List<F>, com.google.common.base.Function<? super F, ? extends T>) and Arrays.asList(Object[])
    
    Creates a view of an array that applies a function to each element.
  - apply
```
public static <T1,R> List<R> apply(List<T1> list,
                                   Function1<T1,R> f)
```
    Creates a copy of a list, applying a function to each element.
  - filter
```
public static <E> List<E> filter(List<E> list,
                                 Predicate1<E> predicate)
```
    Returns a list that contains only elements of list that match predicate. Avoids allocating a list if all elements match or no elements match.
  - exists
```
public static <E> boolean exists(List<? extends E> list,
                                 Predicate1<E> predicate)
```
    Returns whether there is an element in list for which predicate is true.
  - all
```
public static <E> boolean all(List<? extends E> list,
                              Predicate1<E> predicate)
```
    Returns whether predicate is true for all elements of list.
  - generate
```
public static <E> List<E> generate(int size,
                                   Function1<Integer,E> fn)
```
    Returns a list generated by applying a function to each index between 0 and size - 1.
  - ignore0
```
public static <R> Function0<R> ignore0()
```
    Returns a function of arity 0 that does nothing.
    
    Type Parameters:
    
    R - Return type
    
    Returns:
    
    Function that does nothing.
  - ignore1
```
public static <R,T0> Function1<R,T0> ignore1()
```
    Returns a function of arity 1 that does nothing.
    
    Type Parameters:
    
    R - Return type
    
    T0 - Type of parameter 0
    
    Returns:
    
    Function that does nothing.
  - ignore2
```
public static <R,T0,T1> Function2<R,T0,T1> ignore2()
```
    Returns a function of arity 2 that does nothing.
    
    Type Parameters:
    
    R - Return type
    
    T0 - Type of parameter 0
    
    T1 - Type of parameter 1
    
    Returns:
    
    Function that does nothing.
  - nullsComparator
```
public static <T extends Comparable<T>> Comparator<T> nullsComparator(boolean nullsFirst,
                                                                      boolean reverse)
```
    Returns a Comparator that handles null values.
    
    Parameters:
    
    nullsFirst - Whether nulls come before all other values
    
    reverse - Whether to reverse the usual order of Comparables
  - identityComparer
```
public static <T> EqualityComparer<T> identityComparer()
```
    Returns an EqualityComparer that uses object identity and hash code.
  - arrayComparer
```
public static <T> EqualityComparer<T[]> arrayComparer()
```
    Returns an EqualityComparer that works on arrays of objects.
  - selectorComparer
```
public static <T,T2> EqualityComparer<T> selectorComparer(Function1<T,T2> selector)
```
    Returns an EqualityComparer that uses a selector function.

Class Functions

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

FUNCTION_RESULT_TYPES

FUNCTION1_CLASSES

NULLS_FIRST_COMPARATOR

NULLS_LAST_COMPARATOR

NULLS_LAST_REVERSE_COMPARATOR

NULLS_FIRST_REVERSE_COMPARATOR

IDENTITY_COMPARER

ARRAY_COMPARER

CONSTANT_NULL_FUNCTION1

TO_STRING_FUNCTION1

Constructor Detail

Functions

Method Detail

map

inverse

constant

constantNull

truePredicate1

falsePredicate1

truePredicate2

falsePredicate2

identitySelector

toStringSelector

ofTypePredicate

toPredicate2

toPredicate

toPredicate

functionClass

adapt

adapt

adapt

adapt

adapt

adapt

apply

filter

exists

all

generate

ignore0

ignore1

ignore2

nullsComparator

identityComparer

arrayComparer

selectorComparer